Processes executing on the host processor of a network node send messages to peer processes on other nodes by submitting a work request to the network interface controller (NIC) of the node. In response to the work request, NIC driver software running on the host processor generates a corresponding work item, often referred to as a work queue entry (WQE), and queues the item in the host memory for execution by the NIC. To inform the NIC that there is a new WQE awaiting execution, the driver writes a command via the host bus (such as a PCI Express bus) to a doorbell register of the NIC at a bus address that is designated for this purpose. This write operation is referred to as “ringing the doorbell” of the NIC. The NIC responds to the doorbell by fetching the WQE from the host memory and then executing the WQE, which causes the NIC to send a message, comprising one or more data packets, over the network to the peer process that was specified in the work request.